The present invention relates to a medical adhesive composition used for adhesion to the skin in the medical and sanitary fields, and a medical adhesive tape or sheet prepared using this composition.
In general, a medical adhesive composition is applied to one side of a substrate as an adhesive layer, and used by adhesion to the skin in the form of a medical adhesive tape or sheet.
As a conventional medical adhesive composition, an acrylic adhesive containing an acrylic acid alkyl ester as a main component and a rubber adhesive containing a natural rubber and/or a synthetic rubber as a main component have been broadly used.
However, of the above-mentioned adhesive compositions, the rubber adhesives are relatively difficult to handle, because control of the adhesive property thereof is rather difficult, and particularly, natural rubber adhesives potentially cause expression of allergy and the like. Accordingly, acrylate adhesive compositions, which permit easy control of the adhesive property by adjusting composition ratios, amount of additives and the like, have been increasingly studied in recent years.
The present Applicant previously proposed a medical adhesive composition containing a copolymer obtained by copolymerizing a monomer mixture containing an acrylic acid alkyl ester having a C4-C12 alkyl group, (meth)acrylic acid, methacrylic acid alkyl ester having a C1-C4 alkyl group and a multifunctional monomer having two or more unsaturated double bonds in a molecule (JP-A-2002-53461).
The practical property requested of an adhesive layer is an adhesion force that prevents an adhesive tape or sheet from falling from the skin during use, that does not cause a physical pain upon peeling, and that does not easily cause skin irritation. It is of course necessary to have a cohesive force that does not leave an adhesive on the skin upon peeling. However, the adhesiveness and cohesiveness of an adhesive composition are subject to a cancel effect. Accordingly, a medical adhesive composition showing a superior balance between the adhesiveness and cohesiveness has been desired.
It is therefore an object of the present invention to provide an adhesive composition preferable for use as medical and sanitary materials (e.g. adhesive plaster, dressing, drape etc.), which shows a superior balance between an adhesiveness that permits sufficient fixing on the skin and a cohesiveness free of adhesive residue upon peeling, and an adhesive tape or sheet using this composition.
As a result of the intensive studies in an attempt to obtain an adhesive composition capable of satisfying the balance between the adhesiveness and cohesiveness practically necessary as a medical adhesive composition, the present inventors have found that a medical adhesive composition containing a copolymer obtained by copolymerization of a particular monomer mixture, or a monomer mixture obtained by removing a multifunctional monomer having two or more unsaturated double bonds in a molecule from a monomer mixture of the invention of JP-A-2002-53461, and having a particular scope of a gel-sol ratio and a weight average molecular weight of the sol portion is more superior in the balance between the adhesiveness and cohesiveness.
The present inventors have also took note of the correlation shown by the above-mentioned adhesive composition between a gel fraction and a swelling ratio of the gel portion, based on which also found that the above-mentioned adhesive composition having particular ranges of a gel fraction and a swelling ratio of the gel portion is more superior in the practical balance between the adhesiveness and cohesiveness.
Accordingly, the present invention provides the following.
(1) A medical adhesive composition comprising a copolymer obtained by copolymerizing a monomer mixture containing an acrylic acid alkyl ester having C4-C12 alkyl group, a (meth)acrylic acid, and a methacrylic acid alkyl ester having C1-C4 alkyl group, which mixture is free of a multifunctional monomer having two or more unsaturated double bonds in a molecule, wherein the copolymer has a gel-sol ratio of 35:65 to 55:45 and a weight average molecular weight of the sol portion of 300,000 to 500,000 (hereinafter to be also referred to as the present invention 1).
(2) A medical adhesive composition comprising a copolymer obtained by copolymerizing a monomer mixture containing an acrylic acid alkyl ester having C4-C12 alkyl group, a (meth)acrylic acid, and a methacrylic acid alkyl ester having C1-C4 alkyl group, which mixture is free of a multifunctional monomer having two or more unsaturated double bonds in a molecule, wherein the copolymer has a gel fraction of 35 to 55% and a swelling ratio of a gel portion of 50 to 90 times (hereinafter to be also referred to as the present invention 2).
(3) The medical adhesive composition of the above-mentioned (1) or (2), wherein the monomer mixture comprises 1 to 5 parts by weight of the (meth)acrylic acid and 3 to 20 parts by weight of the methacrylic acid alkyl ester, per 100 parts by weight of the acrylic acid alkyl ester.
(4) An adhesive tape or sheet having an adhesive layer made from the medical adhesive composition of any of the above-mentioned (1) to (3) formed on one surface of the substrate in a thickness of 10 to 100 xcexcm.